2003 Ford Fiesta speedometer cutting out

Hi all.

I only bought my car ten months ago, so not sure if the fault was already happening before i bought it. But about 9 months ago when I first started driving my car the speedometer one day stopped working, but cutting in and out. It sometimes works, sometimes doesnt.

The speedometer will move up to zero when you start the car, but will not move from zero once you have started driving. When you turn the engine off, the speedometer will drop back to where it stays when the engine is not started.

However, it only does this occasionally. It has gradually gotten worse and worse though.

It first started off, that the speedometer would not work about once a month, and it would only not work when you had first gotten in the car. However, now the speedo will drop about three times during one ten minute journey in the car.

What i mean by when I say it would only not work when your first get in the car, was now even when you have started the car and it has been working and you have been driving for say 5 minutes, it will drop in the middle of a journey. It never used to do this, if it wasnt working when you first started driving then you new it wasnt going to work for the journey. If you started the car and the speedometer was working, you used to be able to know that the speedo would work for the whole journey. Now it cuts out more often and when your driving, stopped still for seconds, anytime really.

Another problem is that sometimes, my mileage that is displayed under the speedometer will disapear. It will just show ---- instead of my mileage. When it does this though, the speedometer will usually not work for days (longest being 3 days) Then when the speedo kicks back in, so will the mileage. When the mileage is still being shown and the speedo is not working, then usually it will only not work for a short period of time. (Anything from a second to a few hours.)

We have checked all of the earths,(As I have central locking problems. Usually the button on my key wont work when the speedo is not working) taken the clocks out and checked the connection, tightened all of the connections, check the speedo itself and the speedo connection. We disconnected the speed sensor and the speedo obviously didnt work, but the mileage was still being shown, so we dont think it is the sensor. As the mileage does not show when the speedo is broken for a long period of time.

Anyone got any ideas what this could be?